In the recently growing market for mobile devices, such as mobile phones, PDAs, the diversity in functionalities and user interfaces have increased so that in most existing mobile devices a display (for example a Liquid Crystal Display LCD) is provided having a cursor which is to be controlled by the user usually by means of a 5-way joystick. Such a joystick may contain five switches located under the dome of a knob which is to be operated by the user for obtaining the movement of the cursor on the display. One of four switches is closed depending upon moving the joystick which constitutes a movable object, to the left or right side. A “click” function can be obtained in conjunction with the fifth switch based on an operation of the user pressing the joystick vertically depending upon a certain item on a menu where the cursor is actually positioned.
Mobile devices as mentioned above may have an increasingly larger display, and the control menu of such devices becomes more and more complex. A continuous and highly sensitive and reliable control of the cursor by means of the joystick is required. Moreover, such a joystick for mobile devices must be compact, robust, must have a low power consumption and also a low price.
In this connection, reference WO 2007/122556 A2 discloses a detection circuit for detecting movements of a movable object such as a joystick, wherein a plurality of first detection units is provided for detecting the presence or absence of a light spot on the detection units, the light spot being influenced in its position by the movement of the movable object. Second detection units are provided for detecting light intensities of the light spot depending upon a movement of the movable object in a further direction. Specifically, two intensities of the light spots are detected by the second detection units, and an output signal is obtained indicative of a movement of the movable object in a Z-direction representing the click function of the joystick arrangement. The output signals of the detection units are compared with corresponding reference signals, resulting in a one bit digital signal. The signals are digitalized at every photodetector of the detection units to obtain the digitalized signal ready for further data evaluation. The detection units comprise photodiodes and transistors for digitizing the signals from the photodiodes.